An independent confirmation of the future flyby of Gliese 710 to the solar system using Gaia Dr2

Gliese 710 is a K7V star located 19 pc from the Sun in the constellation of Serpens Cauda (Gray et al., 2006). It has been known for nearly two decades that Gliese 710 is headed straight for the solar system (García-Sánchez et al., 1999; Matese & Lissauer, 2002; Bobylev, 2010; Feng & Bailer-Jones, 2015; Berski & Dybczyński, 2016). The most recent published analysis, based on Gaia DR1, concluded that in $1.35\pm 0.05$ Myr, Gliese 710 will be $13366\pm 6250$ au from the Sun (Berski & Dybczyński, 2016). Here, we present an independent confirmation of this remarkable result using Gaia DR2. Our approach is first validated using as test case that of the closest known stellar flyby, by the binary WISE J072003.20-084651.2 or Scholz’s star (Mamajek et al., 2015).

Gaia DR2 (Gaia Collaboration et al., 2016, 2018) provides, among other data, right ascension and declination, absolute stellar parallax, spectroscopic radial velocity, proper motions in right ascension and declination, and their respective standard errors, all in the solar barycentric reference frame. These data can be transformed into equatorial values as described by e.g. Johnson & Soderblom (1987); state vectors in the ecliptic and mean equinox of reference epoch suitable for solar system numerical integrations can subsequently be computed by applying the usual transformation that involves the obliquity. Using input data from Gaia DR2 and barycentric Cartesian state vectors for the solar system provided by Jet Propulsion Laboratory’s horizons,³³3https://ssd.jpl.nasa.gov/?horizons we have carried out $N$-body simulations as described by de la Fuente Marcos & de la Fuente Marcos (2012). Both input data and integration tools are different from those used in previous works.

For validation purposes, we have used the flyby of Scholz’s star investigated by Mamajek et al. (2015) as test case; this work states that WISE J072003.20-084651.2 may have passed ${0.25}_{-0.07}^{+0.11}$ pc from the Sun, ${70}_{-10}^{+15}$ kyr ago. We have used the same input data (Scholz’s star has no public data in Gaia DR2) and our independent approach to compute the evolution backward in time of 1000 control datasets of this star. Figure 1, top panel, shows our results: the perihelion distance is $r=0.28\pm 0.12$ pc and it happened $t_r=73\pm 14$ kyr ago (averages and standard deviations, the median and interquartile range, IQR, values are $0.25\pm 0.12$ pc and $71\pm 16$ kyr, respectively), the closest approach might have reached 0.09 pc or 19 312 au, 43 kyr ago. Our results are consistent with those in Mamajek et al. (2015). Applying identical methodology to Gliese 710, but this time using input data from Gaia DR2 (object Gaia DR2 4270814637616488064) and integrations forward in time, we obtain Figure 1, bottom panel: now $r=0.052\pm 0.010$ pc (or $10721\pm 2114$ au) and $t_r=1.28\pm 0.04$ Myr into the future (averages and standard deviations, the median and IQR values are $0.052\pm 0.013$ pc and $1.28\pm 0.05$ Myr, respectively), the closest approach might reach 0.021 pc or 4303 au, in 1.29 Myr (using older input data, we obtain $r=0.06\pm 0.02$ pc and $t_r=1.35\pm 0.03$ Myr).

Our results confirm, within errors, those in Berski & Dybczyński (2016), but suggest a closer, both in terms of distance and time, flyby of Gliese 710 to the solar system. Such an interaction might not significantly affect the region inside 40 au as the gravitational coupling among the known planets against external perturbation can absorb efficiently such a perturbation (Innanen et al., 1997; Tanikawa & Ito, 2007), but it may trigger a major comet shower that will affect the inner solar system (see e.g. Mamajek et al. 2015; Berski & Dybczyński 2016; Królikowska & Dybczyński 2017; de la Fuente Marcos et al. 2018).

We thank S. J. Aarseth for providing the code used in this research and A. I. Gómez de Castro for providing access to computing facilities. This work was partially supported by the Spanish MINECO under grant ESP2015-68908-R. In preparation of this Note, we made use of the NASA Astrophysics Data System. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.